1. Field of the Invention
The present invention generally relates to a tape cassette for accomodating a reeled length of magnetic recording tape utilized for recording or reproducing information such as music, thereon or therefrom, respectively. More particularly, the present invention relates to the tape cassette having tape cleaners for cleaning the reeled length of magnetic recording tape as the latter travels from one reel to the other reel.
2. Description of the Prior Art
As a means for digitally recording or reproducing information such as, for example, music, a digital signal recording or reproduction with the use of a fixed magnetic head is well known. In terms of a high fidelity sound recording or reproduction, it is very important for the digital recording and/or reproducing system to reproduce the information at as small an error rate as possible. The error rate referred to previously and hereinafter is defined as meaning the rate of the number of error signals relative to the number of data read from a length of magnetic recording tape which has been recorded with signals.
The tape cassette generally includes tape guides which are held in sliding contact with the reeled length of magnetic recording tape when the tape cassette is in use with the length of magnetic recording tape travelling from one reel to another. A long term use of the tape cassette often results in an accumulation, inside the tape cassette, of shavings of one or both of the tape guides and the length of magnetic recording tape due to repeated sliding contact therebetween and also of dust having entered the tape cassette. The foreign matter such as the shavings and/or the dust accumulated within the tape cassette are apt to adhere to a recording surface of the magnetic recording tape which is scanned by the magnetic head, and therefore, when the magnetic head scans a recorded track of the magnetic recording tape, the magnetic head gives rise to an increased error rate.
It has been found that, when information was digitally recorded and then reproduced from the length of magnetic tape contained in the prior art tape cassette, the error rate has been found to be high at 5.times.10.sup.-3 which is detrimental to the quality of products, that is, cassette magnetic tapes, for use in digital information recording or reproduction.
In an effort to substantially eliminate the above discussed problem, the inventors of the present invention have suggested in Japanese Patent Application No. 4-22392, filed Feb. 7, 1992, in Japan (corresponding to U.S. patent application Ser. No. 08/013,378 entitled "TAPE CASSETTE" and filed Feb. 4, 1993, in the name of M. Watanabe et al.), the use of a tape cleaner made of a piece of non-woven fabric within the tape cassette.
According to the above mentioned prior application, the error rate has successfully been reduced to a stable value on the order of 10.sup.-5. In the tape cassette disclosed in the prior application, the tape cassette includes a pair of generally rectangular flat panels, and a peripheral wall disposed between the top and bottom panels to keep them spaced apart a distance sufficient to accommodate a length of magnetic recording tape within the casing and including front and rear wall sections and a pair of side wall sections, all assembled together to cause the tape cassette to represent a generally rectangular, generally flattened box-like configuration. The front wall section of the magnetic tape cassette has at least three access windows defined therein; first and second pinch roller access windows and a head access window positioned midway between the first and second pinch roller access windows.
Within the tape cassette, there is disposed a pair of freely rotatable reels to which opposite ends of the length of magnetic recording tape are anchored, respectively; a pair of guide rollers rotatably disposed at respective corner areas adjacent the front wall section; a generally elongated tape guide rockably disposed generally parallel to the front wall section and extending between the guide rollers; a magnetic shield piece fixedly carried by the tape guide so as to confront the head access window; a perforated guide unit carried by the tape guide so as to confront the head access window; and a pressure pad carried by the tape guide via a leaf spring resiliently urging the presser pad to protrude through the perforation in the guide unit towards the head access window to thereby ensure a positive contact between the magnetic head and a portion of the length of magnetic recording tape traversing the presser pad. All these elements are accommodated and disposed therein in a manner well known to those skilled in the art.
The tape cleaner disclosed in the above mentioned prior application comprises a generally rectangular plastics backing or film and a piece of non-woven fabric rigidly mounted on the plastic backing. This tape cleaner is disposed at the corner regions adjacent the front wall section and in close proximity to the guide rollers. The piece of non-woven fabric is normally urged towards the respective guide roller against the resiliency of the corresponding plastic backing so that, during travel of the length of magnetic recording tape from one reel to the other reel, the recording surface of the magnetic recording tape can be cleaned in sliding contact with the associated piece of non-woven fabric as it passes around the respective guide roller.
In another embodiment disclosed in the prior application, a pair of tension pins are employed within the tape cassette and the pieces of non-woven fabric are utilized to cooperate with the respective tension pins in place of the guide rollers.
Subsequent studies have revealed that the tape cassette disclosed in the prior application has some problems associated with tension present in the length of magnetic recording tape accommodated therein. Specifically, since the tape cleaners are resiliently urged towards the associated guide rollers or tension pins with portions of the length of magnetic recording tape slidably sandwiched between the pieces of non-woven fabric and the guide rollers or the tension pins, not only does a smooth rotation of one or both of the guide rollers tend to be hampered, but a relatively high frictional resistance is developed between each of the pieces of non-woven fabric and the relevant portion of the length of the magnetic recording tape. A measurement of the tension under which the length of magnetic recording tape is held during the travel thereof from one reel to the other reel (hereinafter referred to as tape tension) has been shown to be very high at 40 grams.
If the tape tension is too high, a drive mechanism used in a cassette tape deck or a cassette tape player to drive a capstan must be of a type capable of providing a high driving force to be transmitted to the length of magnetic recording tape as the latter is driven while sandwiched between the capstan and the associated pinch roller. This means that the drive mechanism must have a high load capacity and will thus consume a relatively large amount of electric power, and the increased power consumption is indeed detrimental particularly to a battery-operated compact and/or portable cassette tape player since the length of running time during which the cassette tape player is available for actual information recording and reproduction is shortened.